The present invention relates generally to instruments for chemical reaction control, product and reactant manipulations, detection of participating reactants and resultant products, and more particularly to integrated microfabricated instruments which perform microscale chemical reactions involving precise control of parameters of the reactions. The parameters of the reaction controlled by the instrument may be temperature, pressure, concentration of reactants, the intensity or frequency of incident light, electromagnetic fields, or ultrasonic pressure waves, etc.
The term “integrated microfabrication” is used herein to refer to all processes used for batch production of semiconductor microelectronics, and all related microfabrication processes such as LIGA (see R. S. Muller, R. T. Howe, S. D. Senturia, R. L. Smith, and R. M. White, ed. MICROSENSORS, IEEE Press, 472 pages, 1990). Microfabrication technologies include, but are not limited to, sputtering, electrodeposition, low-pressure vapor deposition, photolithography and etching. Microfabricated devices are usually formed on crystalline semiconductor substrates such as silicon or gallium arsenide. Noncrystalline materials such as glass or certain polymers may be used although crystalline materials provide certain advantages. The shapes of crystalline devices can be precisely controlled since etched surfaces are generally crystal planes, and crystalline materials may be bonded by processes such as fusion at elevated temperatures or the field-assisted method (Mallory bonding). Materials which are not semiconductors, such as quartz or glass, may be used, though semiconductor materials provide the advantage that electronic circuitry may be integrated into the system by the use of conventional integrated-circuit fabrication techniques.
Monolithic microfabrication technology now allows the production of electrical, mechanical, electromechanical, optical, chemical and thermal devices including pumps, valves, heaters, mixers and species detectors for microliter to nanoliter quantities of solids, liquids and gases. Microscale sensors include optical waveguide probes and ultrasonic flexural-wave sensors. The integration of these devices into a single system allows for the batch production of microscale reactor-based analytical instruments. Integrated microinstruments may be applied to biochemical, inorganic, or organic chemical reactions to perform biomedical and environmental diagnostics, and biotechnological processing and detection.
Such integrated microfabricated devices can be manufactured in batch quantities with high precision, yet low cost, thereby making recyclable and/or disposable single-use devices practical. Alternatively, the instrument may consist of an array of reaction instruments which are to operate in parallel to simultaneously perform a number of related reactions. Operation of such instruments is easily automated, further reducing costs. Since the analysis can be performed in situ, the likelihood of contamination is very low. Because of the inherently small sizes of such devices, the heating and cooling can be extremely rapid, and the devices can have very low power requirements. Such devices may be powered by batteries or by electromagnetic, capacitive, inductive or optical coupling.
Small volumes and high surface-area to volume ratios provide microfabricated reaction instruments with a high level of control of the parameters of a reaction. Heaters may produce temperature cycling or ramping, sonochemical and sonophysical changes in conformational structures may be produced by ultrasound transducers, and polymerizations may be generated by incident optical radiation.
Synthesis reactions, and especially synthesis chain reactions, such as the polymerase chain reaction (PCR) or the ligase chain reaction, are particularly well-suited for microfabricated reaction instruments. PCR can selectively amplify a single molecule of DNA (or RNA) of an organism by a factor of 106 to 109. This well-established procedure requires the repetition of heating (denaturing) and cooling (annealing) cycles in the presence of an original DNA target molecule, specific DNA primers, deoxynucleotide triphosphates, and DNA polymerase enzymes and cofactors. Each cycle produces a doubling of the target DNA sequence, leading to an exponential accumulation of the target sequence. PCR-based technology has been applied to a variety of analyses, including environmental and industrial contaminant identification, medical and forensic diagnostics, and biological research.
The procedure involves: (1) processing of the sample to release target DNA molecules into a crude extract; (2) addition of an aqueous solution containing enzymes, buffers, deoxyribonucleotide triphosphates (dNTPS), and oligonucleotide primers; (3) thermal cycling of the reaction mixture between two or three temperatures (e.g., 90–96, 72, and 37–55° C.); and (4) detection of amplified DNA. Intermediate steps which incorporate signal-producing and/or surface-binding primers, or which purify the reaction products, via, for example, electrophoresis or chromatography may be introduced. A problem with standard PCR laboratory techniques is that the PCR reactions may be contaminated or inhibited by introduction of a single contaminant molecule of extraneous DNA, such as those from previous experiments, or other contaminants, during transfers of reagents from one vessel to another.
PCR reaction volumes are presently typically on the order of 50 microliters. A thermal cycle typically consists of heating a sample to a first temperature, maintaining the sample at the first temperature, cooling the sample to a second lower temperature, and maintaining the temperature at that lower temperature. The rate at which the sample is heated is generally limited by the heater rather than the rate of heat transfer to the sample. Presently, each of the four stages of a thermal cycle requires approximately one minute, and the time required for twenty to forty complete thermal cycles is therefore from about one to three hours. The cycling time has been reduced by performing the PCR reaction in capillary tubes (see C. T. Wittwer, G. C. Fillmore, and D. J. Garling, Analytical Biochemistry, 186, pp. 328–331 (1990)). A high-power forced air heater was used to heat the tubes. The thinnest capillary tubes contained a sample volume of about ten microliters. Each cycle consisted of a heating step, a waiting period, a cooling step and another waiting period, and each step required approximately fifteen seconds.
Although the PCR reaction requires thermal cycling of the reagents, any reaction that benefits from precise temperature control, and/or rapid thermal cycling, thermal ramping, or any other temperature variation of reagents with time (hereinafter to be referred to as temperature programming) will be well suited for the microfabricated reaction instrument of the present invention.
An object of the present invention is therefore to provide a integrated microfabricated reactor.
Another object of the present invention is to provide a reactor-based instrument for inorganic, organic and biochemical reactions, and in particular for diagnostics.
Another object of the present invention is to provide a reactor which provides high-precision control of reaction parameters.
Another object of the present invention is to provide a reactor which provides high-precision temperature control.
Another object of the present invention is to provide a reactor which provides rapid high-precision thermal cycling, ramping or programming.
Another object of the present invention is to provide a closed system reactor which is self-contained, e.g. which is shipped from the factory containing the reagents, thereby minimizing the susceptibility to contamination.
Another object of the present invention is to provide low-cost reaction and/or detection systems.
Another object of the present invention is to provide an instrument for in situ reactions which may be powered by incident electromagnetic radiation or batteries.
Another object of the present invention is to provide arrays of microfabricated reaction chambers which may operate in parallel or series.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.